The present invention is directed toward a backup power supply for a crash-survivable data memory unit that is capable of providing continued operation of the device upon loss of electrical power.
The Federal Aviation Administration requires that most commercial aircraft be equipped with a crash-survivable flight data recorder (FDR) and cockpit voice recorder (CVR). Such systems collect vital flight information that provides evidence for the reconstruction and analysis of a subsequent accident. The FDR and CVR is usually powered from a vital electrical bus to ensure operation in all foreseeable operating configurations.
There have been several aircraft accidents in which FDR and CVR recording was discontinued prior to the crash, due to a loss of some or all electrical systems in the aircraft. In these cases, the National Transportation and Safety Board (NTSB) noted that continued operation of either recorder during the power outage could have provided accident investigators with valuable information regarding the cause of the crash.
In its Mar. 9, 1999 letter to the FAA, the NTSB has recommended that, starting in 2005, all aircraft that are required to carry CVRs and FDRs be fitted with an independent power source that is located with the CVR, and automatically engages to provide ten minutes of operation whenever aircraft power to the recorder ceases, either by normal shutdown or through an electrical bus failure/loss. In addition, the NTSB has recommended that all aircraft manufactured after Jan. 1, 2003 be equipped with dual combination (CVR/FDR) recording systems, each powered from a separate, reliable aircraft power supply. Each requirement is an attempt to ensure that FDR and CVR data is recorded during aircraft power outages. There are no systems in the present art, however, that meet the first recommendation, and the second recommendation would be ineffective in collection of data in the event of a total aircraft loss of power.
Backup power sources for FDRs and CVRs have not been previously developed for several reasons. First, older FDRs and CVRs, many of which are still in the field, store data on a continuously-driven magnetic tape. The electrical power required to operate such tape drives, even for a short period of time, requires large and heavy power storage devices that are infeasible for aircraft. Second, a power backup to the CVR and/or FDR could have negative consequences if power to the recorder continues after a crash, allowing it to overwrite vital data in doing so. Finally, the FDR can continue to receive useful data during a power loss only if the sensors supplying it also retain power. The complexity and variation in modern aircraft electrical systems prevents a feasible supply of power to the sensors. Because the CVR and FDR power problems are linked, a division of the backup power supplies for them was deemed an incomplete solution to the overall problem. For at least these reasons, backup power supplies for the FDR and CVR have not been mandated by the NTSB, nor have they been installed on aircraft.
The present invention recognizes and utilizes recent developments in several fields of invention to make possible a backup power supply for vehicle data acquisition and recording systems. For example, traditional magnetic tape storage units have been largely replaced by low-power solid state memory devices. Thus, the size of a backup power storage device that will supply the required amount of power is much smaller, making it feasible for installation in aircraft. In addition, the development of lithium batteries has reduced the size and weight of batteries for a given energy storage requirement. These aspects combined with new smaller and lighter FDR/CVR designs, as described in U.S. Pat. No. 6,153,720 and incorporated herein, make it feasible to incorporate an additional backup power supply into an FDR or CVR as taught by the present invention.
According to one aspect of the present invention, the problems of supplying backup power to FDRs and CVRs are identified by analyzing the specific and different power needs of FDRs and CVRs. Aspects of FDR and CVR operation, during startup, operating, shutdown, accident phase, and post-crash phase are defined. According to another aspect of the invention, a system that ensures reliability of power and continuity of important data acquisition throughout each of the aforementioned phases is described, as summarized in the following paragraphs.
According to yet another aspect of the present invention, a device is disclosed that provides backup electrical power for a vehicle data acquisition and recording system. The device includes a charging control circuit, a discharge control circuit, and a power storage element. The invention receives charging power from an external vehicle electrical bus, and maintains a continuity of power to the recording system in the event of a loss of said bus.
According to still another aspect of the present invention, a method is disclosed for providing backup electrical power for a vehicle data acquisition and recording system, by delineating a process in which a vehicle electrical bus is monitored for power availability, and the system operates either in charging or discharging mode depending on the status of the bus. In addition, a process step includes monitoring the duration of a discharge cycle, and causes a discontinuation of power to the recording system after a pre-determined interval, to ensure that vital data is not over-written after an accident.
These and other aspects of the present invention are described further in the detailed description of the preferred embodiments of the invention which follow.